JPH0623553A - Manufacture of welded steel tube - Google Patents

Abstract

PURPOSE:To improve the applying capacity of the existing welding line by improving welding speed by using gaseous CO2 shielded arc welding in combination with submerged arc welding. CONSTITUTION:A steel strip is formed in a spiral state and submerged arc welding S1 is executed to the butting parts from an inner side. When the welded part holds >=150 deg.C, gaseous CO2 shielded arc welding G1 is executed from an outside, further, submerged arc welding S2 is executed. Consequently, load on the submerged arc weldings S1, G1 is reduced by gaseous CO2 arc shielded arc welding G1, high speed welding can be made, welding defects given when CO2 gas shielded arc welding G1 is applied at a high speed, can be prevented by the holding heat of the preceeding submerged arc welding part and the manufacturing speed of a welded steel tube can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a welded steel pipe capable of obtaining a high-speed and sound weld, and more particularly to a method suitable for producing a spiral steel pipe.

[0002]

2. Description of the Related Art Welded steel pipes are roughly classified into electric resistance welded pipes, forged steel pipes and submerged arc welded steel pipes. Submerged arc welded steel pipe is usually large diameter steel pipe, spiral steel pipe is UO
It is considered to be a representative of submerged arc welded steel pipe together with E steel pipe.

As is well known, the manufacture of spiral steel pipe is as follows.
It is performed by forming a steel strip in a spiral shape and subjecting side edge butting portions to submerged arc welding from the inner surface side and the outer surface side, respectively. The manufacturing speed of submerged arc welded steel pipes is slower than the manufacturing speed of other welded steel pipes, and in the manufacture of spiral steel pipes, each electrode on the inner and outer surfaces is made into multiple electrodes and welding is performed in one pass inside and outside to improve efficiency. I am trying.

However, as the plate thickness increases, the welding speed rapidly decreases, and in the manufacture of thick-walled spiral steel pipes used for steel pipe piles, the line speed must be reduced and full use of the line capacity is required. The current situation is that it cannot be done.

This is because as the plate thickness increases, the welding heat input increases, the pool increases, and it takes time to solidify the pool. Therefore, if the line is moved at high speed, the welded part will rotate without being solidified. This causes the pool to flow and deteriorate the shape of the welded part.

In order to solve this problem, a method of manufacturing a spiral steel pipe using welding other than submerged arc welding has been considered. When welding other than submerged arc welding is used together, the load of submerged arc welding is reduced, and even if the plate thickness increases, the welding heat input in submerged arc welding is kept small and the pool does not increase.
Therefore, the welding speed can be increased.

As a method of realizing such an idea, a method of manufacturing a spiral steel pipe using electric resistance welding together is disclosed in Japanese Patent Laid-Open No. 60-21180. Although not intended to improve the welding speed, the use of AC MIG welding together improves the quality of the welded area.
A method for manufacturing an O steel pipe is disclosed in "Iron and Steel No. 71 (1985) No. 3 P505-507".

[0008]

However, in the method for manufacturing a spiral steel pipe that also uses electric resistance welding, there is a problem in equipment technology of performing electric resistance welding in a spiral pipe line, and in addition, line speed and proper welding are required. There is a problem in welding quality due to the speed mismatch.

That is, the maximum line speed of the current spiral pipe line is suppressed to 5 to 6 m / min due to various restrictions, whereas the proper welding speed of electric resistance welding is significantly higher than that of the current spiral pipe line. In order to perform electric resistance welding on a spiral pipe line, its speed must be reduced to the line speed, which inevitably reduces weldability. Therefore, at present, in addition to the problem of equipment technology, this problem of welding quality must be solved, which is very difficult to implement.

On the other hand, AC MIG welding cannot be used as a means for improving the efficiency because it is impossible to increase the welding speed up to the maximum line speed of the spiral pipe line due to its nature.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a welded steel pipe which can be easily applied to the manufacture of a spiral steel pipe and whose efficiency can be greatly improved. .

[0012]

[Means for Solving the Problems] In order to improve the manufacturing efficiency of spiral steel pipes, it is considered indispensable to use welding other than submerged arc welding together. Because
In submerged arc multi-layer welding, slag is present between the layers, which causes a problem such as separation of the welded portion. Therefore, welding other than submerged arc welding in which slag does not occur is required. However, electric resistance welding has technical difficulties as mentioned above,
High-speed welding is impossible in AC MIG welding.

Therefore, the present inventors have paid attention to carbon dioxide gas arc welding among gas metal arc welding, and investigated the suitability as a means for improving the efficiency in manufacturing spiral steel pipes from various angles. As a result, it was found that the combined use of carbon dioxide arc welding can obtain a welded portion quality at a high speed without any problem even when the plate thickness is large, and can significantly improve the welding speed.

According to the method for producing a welded steel pipe of the present invention, the steel strip is formed into a tubular shape, and the abutting portion is subjected to submerged arc welding from either the inner surface side or the outer surface side. With the temperature of
Carbon dioxide arc welding is performed from the other side, and submerged arc welding is performed from above.

Here, the above submerged arc welding can be replaced with carbon dioxide gas arc welding.

FIG. 1 is a plan view of a spiral pipe line showing an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing stepwise a process of forming a welded portion in the present invention.

In FIGS. 1 and 2, reference numeral 1 denotes a steel strip having a Y groove formed on the outer surface of the pipe. When the steel strip 1 is formed in a spiral shape, submerged arc welding S1 is performed from the inner surface side to the abutting portion at the lowermost portion of the spiral tube 2. At the position where the welded portion s1 moves a half turn from the welding position to reach the uppermost portion of the spiral tube 2, carbon dioxide arc welding G1 is performed from the outer surface side. Then, the welded portion g1 further moves one round from the welding position, and the spiral tube 2 is again moved.
At the position reaching the uppermost portion of the above, submerged arc welding S2 is performed on the welded portion g1 from the outer surface side. As a result, the submerged arc welds s1 and s as shown in FIG.
A pipe-made weld having a carbon dioxide gas arc weld g1 interposed between the two is obtained.

When carbon dioxide gas arc welding is performed instead of the submerged arc welding S1, the carbon dioxide gas arc welds g1 and g2 and the submerged arc weld s1 are transferred from the inner surface side to the outer surface side as shown in FIG. 2 (b). A pipe-making welded portion formed in order is obtained.

[0019]

In the method for manufacturing a welded steel pipe of the present invention, carbon dioxide gas arc welding is used in combination with submerged arc welding.

Unlike metal electric arc welding, gas metal arc welding such as carbon dioxide arc welding is easy to carry out on a spiral pipe line. Among them, carbon dioxide arc welding is different from other gas metal arc welding (MIG welding, TIG welding) in that it uses large current welding due to the use of a large diameter wire,
High speed welding is also possible. However, in high-speed carbon dioxide arc welding, poor fusion is likely to occur at the bottom of the weld.

The method for producing a welded steel pipe of the present invention is intended to prevent the fusion failure in the high-speed carbon dioxide gas arc welding and speed up the welding.

That is, in the method for manufacturing a welded steel pipe of the present invention, as shown in FIG. 2 (a), the carbon dioxide gas arc welded portion g1 is formed on the submerged arc welded portion s1 from the back side thereof. Therefore, the bottom portion of the carbon dioxide gas arc weld g1 is fused and integrated with the submerged arc weld s1. At this time, the submerged arc welded portion s1 has only a half circumference of the circumference of the spiral tube 2 after welding, and has sufficient welding heat. Therefore, carbon dioxide arc welding is carried out on a sufficiently preheated base metal.
Therefore, also in the case of high-current high-speed welding using a large-diameter wire, defective fusion of the bottom portion of the weld g1 is prevented.

However, when the temperature of the submerged arc weld s1 is lower than 150 ° C. at the stage of performing carbon dioxide arc welding, in the high-current high-speed welding using a large-diameter wire, there is a fusion defect at the bottom of the weld g1. May occur. However, in a general spiral pipe manufacturing line, carbon dioxide arc welding is performed after moving half the circumference of the submerged arc welding S1 due to the fact that downward welding is adopted. Further, if high speed welding is performed, the time required for moving during this time is further shortened. . Therefore, normally, the residual heat of the submerged arc welding portion s1 is used to perform a high-quality carbon dioxide gas arc welding portion g without a preheating step.
1 is obtained.

When carbon dioxide gas arc welding G1 is performed in place of the submerged arc welding S1, the large current high-speed welding using a large-diameter wire causes defective welding at the bottom of the weld g1. However, the bottom portion thereof is remelted by the next carbon dioxide gas arc welding G2, and the bottom portion of the welded portion g2 of the next carbon dioxide gas arc welding G2 is of quality due to the residual heat of the welded portion g1 of the previous carbon dioxide gas arc welding. Is guaranteed.
Therefore, in this case as well, no defect is generated in the carbon dioxide gas arc welded portions g1 and g2 due to the speedup.

The method for producing a welded steel pipe of the present invention was developed based on the above findings. For example, in the production of a spiral steel pipe, 5 m / min even when the plate thickness exceeds 10 mm.
The above welding speed can be secured.

It is advantageous that the diameter of the welding wire is smaller in comparison of the deposition rates under the same current. If it is less than 3.2 mm, the upper limit of the current value that can be used is low, so a sufficient amount of welding cannot be secured. On the other hand, if it exceeds 4.8 mm, the current value for stabilizing the arc at a high speed becomes very large, and the welding speed is not sufficient. Therefore, the wire diameter is preferably 3.2 to 4.8 mm. This diameter is considerably larger than the wire diameter normally used for carbon dioxide arc welding (around 1.2 mm).

[0027]

EXAMPLES Examples of the present invention will be described below.

A spiral steel pipe for piles having an outer diameter of 609.6 mm and a thickness of 9 to 19 mm, which is defined as STK490 in JIS G3444, is manufactured by the method for manufacturing a welded steel pipe according to the present invention, and the maximum speed thereof is investigated to obtain a conventional method. Compared to the top speed. The maximum speed is the maximum welding speed (maximum line speed) at which a sound weld can be obtained. The results are shown in Table 1 and the welding conditions are shown in Table 2.

In Table 1, A represents a conventional example in which submerged arc welding (SAW) was performed from the inside and outside, and B represents submerged arc welding (SAW) from the inner surface side, carbon dioxide arc welding (GMAW) and submerged arc welding from the outer surface side ( S
AW) is an example of the present invention, and C is an example of the present invention in which carbon dioxide arc welding (GMAW) is performed from the inner surface side, carbon dioxide arc welding (GMAW) and submerged arc welding (SAW) are performed from the outer surface side.

[0030]

[Table 1] * Upper limit line speed () Measured temperature of the previous weld during GMAW

[0031]

[Table 2]

The upper limit line speed of the spiral pipe line used in this example is 5.6 m / min. In the conventional example, when the plate thickness exceeds 10 mm, the maximum speed is extremely reduced, and the line capacity cannot be fully used. However, in the example of the present invention, the maximum speed reaches the upper limit line speed when the plate thickness is 9 mm, and if there is no upper limit, higher pipe manufacturing efficiency can be obtained. Even if the plate thickness exceeds 10 mm, the maximum speed close to the upper limit line speed was obtained, and the line capacity could be fully used.

Although the above embodiment is a method for manufacturing a spiral steel pipe, the present invention is not limited to this, but can be widely applied to the manufacturing of submerged arc welded steel pipes such as UO steel pipes.

[0034]

As is apparent from the above description, the welding steel pipe manufacturing method of the present invention uses carbon dioxide gas arc welding together with submerged arc welding to easily and significantly increase the welding speed and use existing lines. Then, it is possible to make full use of its abilities and to exert a great effect on the actual operation.

[Brief description of drawings]

FIG. 1 is a plan view of a spiral pipe manufacturing line showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a step of forming a welded portion in the present invention.

[Explanation of symbols]

 1 Steel strip 2 Spiral tube S1, S2 Submerged arc welding G1, G2 Carbon dioxide arc welding s1, s2 Submerged arc weld g1, g2 Carbon dioxide arc weld

Claims (2)

[Claims] 1. A state in which a steel strip is formed into a tubular shape, and after the submerged arc welding is performed on the abutting portion from either the inner surface side or the outer surface side, the welded portion retains a temperature of 150 ° C. or higher. Then, the carbon dioxide gas arc welding is performed from the other side, and the submerged arc welding is performed from thereover. 2. A state in which a steel strip is formed into a tubular shape, carbon dioxide arc welding is performed on the abutting portion from either the inner surface side or the outer surface side, and the welded portion retains a temperature of 150 ° C. or higher. Then, the carbon dioxide gas arc welding is performed from the other side, and the submerged arc welding is performed from thereover.